Medical needle for use in ultrasound imaging and method of enhancing the visiblity of such a needle to ultrasound

ABSTRACT

A needle inserted into body tissue is rendered visible to a Doppler ultrasound imager by generating a longitudinal oscillation of the fluid column in the needle barrel by means of a transducer which is energised by a signal of frequency 100 Hz to 2 kHz, for example. An image of the needle tip is displayed on a screen.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation of patent application Ser. No. 08/401,625 filedMar. 9, 1995, now U.S. Pat. No. 5,549,112, issued Aug. 27, 1996.

The present invention relates to a hollow medical needle for use inultrasonic imaging and to a method of enhancing the visibility of such aneedle to a Doppler ultrasound imager.

The theory of ultrasonic transmission in biopsy needles is discussed inULTRASONICS Vol. 26, No. 1, 1988 pp 27 to 30.

U.S. Pat. No. 3,556,079 (Omizo) discloses a medical apparatus comprisinga tubular needle within which is mounted an ultrasonic transducer whichmay be a transmitter, a receiver or a combined transmitter and receiver.This transducer is coupled to saline solution within the needle andtransmits and/or detects ultrasound at considerable distances throughbody tissue at a frequency of e.g. 5 MHz which is subsequently reflectedoff e.g. flowing blood in a blood vessel and shifted in frequencyaccording to the Doppler equation. If the transducer in the needle is atransmitter only, then an external ultrasound receiver is arranged todetect the reflected Doppler-shifted ultrasound which is demodulated togenerate an audio signal whose amplitude is a maximum when the needle isdirected at the blood vessel. However the above arrangement merelyenables the position of the blood vessel or other target to be detectedand does not enable the position of the needle to be detected. It couldnot, for example, be used to direct a needle towards a portion ofdiseased static tissue. Furthermore it is not an imaging system.

Ultrasound imaging utilises the principle of sound reflectivity in orderto form images of body organs. These images are displayed on the monitorin grey-scale. Some ultrasound machines also incorporate the principleof Doppler frequency shift which allows moving objects eg red bloodcells in a blood vessel to be imaged. Such vessels can then be assigneda colour according to the direction of movement within them, and theyappear in colour against the grey-scale background of their environs.

It is often desirable to form such an image during treatment with anaspiration or a biopsy needle and it has been found difficult to producea clearly defined image of the needle by this technique. It has beenproposed to apply a transverse vibration to the needle in order toovercome this problem but this does not result in a clear image of theneedle tip.

GB-A-2,157,828 discloses an ultrasonic imaging apparatus comprising aninner needle having a miniature ultrasonic transducer mounted at its tipand an outer tubular puncture needle surrounding and supporting theinner needle. An ultrasonic imager generates an ultrasonic beam whichimpinges on the miniature transducer and the resulting electric outputsignal is either used to trigger a transponder which causes thetransducer to emit a predetermined ultrasonic signal which is detectableand locatable by the imager or to enable circuitry in the imager todetect the position of the needle from the time interval betweenemission and detection of the ultrasonic beam. From this information theposition of the needle can be superimposed on the image. However theabove arrangement is complex and expensive and in general the needle canbe used only with one design of imager.

Further background information is provided in U.S. Pat. No. 5,131,394,EP-A-397,960, EP-A-83,973 (which teaches at p. 7 para 1 the desirabilityof contact between the stylet and the needle) and WO-A-82/03160, whichhowever lies outside the technical field of the present invention.

EP-A-453,251 discloses a biopsy needle having a solenoid coil coupled toa core which is mounted directly on the proximal end of the stylet andarranged to reciprocate the stylet longitudinally at a frequency of e.g.up to 100 Hz in order to render the needle tip visible to Dopplerultrasound. The amplitude of vibration is such that the tip of thestylet oscillates between a position in which it is flush with theopening of the cannula and a position in which it is retracted about 1mm into the cannula.

However the above arrangement in which the vibratory transducer isdirectly coupled to the stylet has the disadvantage that movement of thestylet inevitably causes motion of similar amplitude and frequency inthe cannula, with the result that the motion is not confined to theneedle tip and the Colour Doppler imager assigns a flare of colour tothe entire needle. Furthermore the weight of the solenoid makes theneedle harder to manipulate, an important point when one considers thedegree of accuracy needed to perform certain biopsies.

Accordingly the present invention provides a medical apparatuscomprising:

a) a tubular needle for insertion into body tissue, said needle having abore in communication with said body tissue at a tip region thereof, and

b) a sub-ultrasonic transducer for generating a longitudinal oscillationof a fluid column within said bore at a sub-ultrasonic frequency, saidtransducer being substantially mechanically isolated from said needle.The oscillation generated by the transducer (preferably at an audiofrequency) enhances the visibility of the region of the needle tip toDoppler ultrasound imaging.

Preferably the transducer is remote from the needle and is coupled tothe needle by a flexible tube which contains a further fluid column(preferably an air column) coupled to the transducer. Such an elasticcoupling enables the tissue to be characterised by its Doppler image, asdescribed below in detail.

In another aspect the invention provides a kit of parts for the aboveapparatus.

In another aspect the invention provides a method of enhancing thevisibility to Doppler ultrasound imaging of the tip and/or adjacenttissue of a tubular needle inserted into a human or animal bodycomprising generating a longitudinal oscillation of a fluid columnwithin said needle at a frequency which is lower than the frequency ofthe ultrasound emitted by the Doppler ultrasonic imager by means of atransducer which is substantially mechanically isolated from the needle.

Since the colour of a region of a Doppler ultrasound image is dependenton the velocity of the corresponding region of tissue and this velocitywill vary with the amplitude of the oscillation of the end of the fluidcolumn at the needle tip (assuming that the period of the oscillation isfixed) and this amplitude in turn is dependent on the mechanicalproperties of the tissue being vibrated by the fluid column, theapparatus of the present invention should enable the tissue at theneedle tip to be characterised. For example, fatty tumours will vibratedifferently from solid lesions and would be expected to generate adifferent colour response in the Doppler image of the needle tip.

Accordingly, in another aspect the invention provides a method ofenhancing the visibility to Doppler ultrasound imaging of the tip and/oradjacent tissue of a tubular needle inserted into a human or animalbody, comprising generating a longitudinal oscillation of a fluid columnwithin said needle at a frequency which is lower than the frequency ofthe ultrasound emitted by the Doppler ultrasonic imager by means of atransducer which is arranged to vary the amplitude of said oscillationin dependence upon the mechanical properties of the tissue. This is mosteasily achieved by coupling the transducer to a column of air or othergas in a tube which communicates with the bore of the needle.

The transducer may for example comprise a moving coil loudspeakercoupled to the fluid column in the needle bore by a connecting tubewhose cross section decreases towards the needle and thereby amplifiesthe motion of the loudspeaker diaphragm. Alternatively a thermaltransducer such as a spark-gap chamber or a piezoelectric transducer maybe used.

The optimum frequency of the longitudinal oscillation generated by thetransducer of the needle arrangement will depend on the Colour Dopplerultrasonic imager with which it is being used, in particular on thevelocity range detectable by the imager. In a typical Colour Dopplerultrasonic imager the minimum detectable velocity will be of the orderof +/-0.001 m/s and a maximum velocity of about +/-3.8 m/s, with a moreusual range being from +/-0.02 m/s to +/-0.6 m/s. Accordingly it isbelieved that the frequency and amplitude of oscillation should be suchthat the maximum velocity is within ve ranges. With convenientlyachievable amplitudes of oscillation, it is believed that the mostuseful frequencies will be in the audio range i.e. 20 Hz to 20 kHz butthe invention is by no means limited to the above ranges.

Preferred embodiments of the invention are described below by way ofexample only with reference to the accompanying drawing, wherein:

FIG. 1 is a diagrammatic representation of a medical apparatus inaccordance with the invention, and

FIG. 2 is a longitudinal cross-section of another needle arrangement foruse in the arrangement of FIG. 1.

Referring to FIG. 1, which is a purely diagrammatic representation, ahollow needle 1 is shown inserted into body tissue 10. The needlecomprises a 22 gauge tubular cannula 2 having an outside diameter of0.711 mm (0.028") and housing a stylet 3 of 0.457 mm (0.018") diameterwithin the cannula. The tip of the stylet projects about 2 mm beyond thetip 31 of the cannula. The stylet is hollow and has an eccentric opening32 immediately adjacent to its closed bevelled tip. The eccentricopening, which protrudes beyond the end of the 22 gauge housing cannula,allows the oscillating air column to deliver movement to adjacent tissuewhile minimising the possibility of body tissue entering the stylet andoccluding it. This arrangement allows the tip of the stylet to berendered visible to Doppler ultrasound during the insertion of theneedle through tissue. 8 mm flexible pressure tubing 4 connects thehollow stylet with the neck of a funnel member 5 as shown. Alternativelythe stylet 3 may optionally be solid and after passage of the needlethrough tissue, the solid stylet may be removed and the bore of thecannula 2 may be connected directly to the pressure tubing (4') andfunnel member as shown in phantom. The mouth of funnel member 5 iscoupled in an airtight manner to a moving coil loudspeaker 7 whosediaphragm 6 is driven by a signal from a signal generator 8.

Preferably the signal, which may be a pulsed or an oscillating signal,has a period of 0.03 s to 0.001 s. More preferably the signal has asine, square or triangular waveform of frequency 333 Hz to 1 kHz(ideally 400 to 800 Hz e.g. 600 Hz) and a power of a few (e.g. 100) mW.

The body tissue is insonated with an ultrasonic beam 11 by a Dopplerultrasound imager 9, which may for example be an Acuson 128XP10 imager.An image 13 of the needle tip 31 is formed on a screen 12 of the imager.

EXAMPLE

A working model utilising a jelly phantom in place of the body tissue 10was constructed generally as shown in FIG. 1. The components of theworking model were as follows: hollow needles, a hollow stylet, aloudspeaker, signal generator and 50 cm of `pressure` tubing. Theneedles were standard 15 cm Chiba needles (Cook Inc., Bloomington Ind.)in 18, 20, and 22G sizes and the 15 cm hollow stylet was made ofsuperelastic nickel titanium alloy with an inner diameter of 0.406 mm(0.016") (Raychem Corp., Menlo Pk. Calif.). The speaker coil wasmodified from a 127 mm (5 inch) diameter plastic-coned loudspeaker(Tannoy Ltd., Strathclyde, Scotland) and was connected in an airtightarrangement via a funnel to the hollow stylet. The signal generator usedwas a Korg 770 synthesiser (Keio Electronic Laboratory Corporation,Tokyo, Japan). This instrument generates square, triangular andrectangular waveforms at a wide range of audio frequencies. The signalwas amplified through a Realistic SA 1500 audio amplifier (TandyCorporation, Fort Worth, Tx.).

Colour Doppler ultrasound machines used to evaluate the device were anAcuson XP10 (Acuson Ltd.),and a Diasonics Spectra VST (Diasonics Ltd.Milipitas Calif. USA). Testing was done by applying a 3.5 MHz probe to ajelly phantom and immobilising it in position. The pressure tubing wasthen connected directly to the needle barrel (minus its matching solidstylet). The needle was then inserted into the phantom as far aspossible. 5 MHz and 7.5 MHz probes were also used with the needle withsimilar results. Signal was applied to the needle starting at 1Hz andgradually increasing in frequency until colour signal was registered bythe ultrasound machine at a selected pulse repetition frequency and gainsetting.

Results

The needle tip was displayed as a beacon of colour regardless of theangle of incidence of the Doppler beam. Transverse, longitudinal andoblique projections displayed the beacon equally. The colour signal wasnot constant but was found to change hue and to flicker at varying ratesdepending on the frequency of the sound wave applied to the needle. Thisis believed to be caused by an interference pattern at the needle tipbetween the frequency of motion and the pulse repetition frequency ofthe incoming Doppler wave. The needle tip was readily detectable wheninserted fully into the phantom. This corresponded to a depth of 15 cm.No signal other than that at the tip of the needle was registered whenthe needle was stationary.

It was found that a frequency of 600 Hz yielded a beacon of signal whichwas readily detectable at pulse repetition frequencies ranging from 800to 2250 kHz using the Diasonics machine. Within this range, colour gainvalues of between 68 and 80 dB were required to demonstrate a visiblebeacon unaccompanied by colour noise on the screen. There was no visibledifference between sine, square, triangular or rectangular waveforms.Many other frequencies were found to generate detectable signal atvarious pulse repetition frequencies and colour gain settings but 600 Hzwas the single frequency most likely to be detectable in the range ofpulse repetition frequencies described.

Increasing gain values above 80 dB led to colour noise which could bemistaken for the needle tip. Below a pulse repetition frequency of 800kHz useful signal at the tip uncorrupted by colour noise wasdemonstrated only at 400 Hz with this particular apparatus. Above 2,250Hz a similar problem occurred with this particular apparatus. Becausepulse repetition frequencies are not given a numerical value on theAcuson XP10 display it was not possible to directly correlate thefindings between it and the Diasonics Spectra VST. It was found that theAcuson machine was capable of displaying the colour beacon at the tip ofthe needle as well as the Diasonics although differences in frequencyresponse between these two machines could not be ruled out because thefrequency of pulse repetition is not displayed on the Acuson machine.

At higher pulse repetition frequencies (greater than 1000 Hz) tissuemotion `flash` was not prominent and did not obscure the signal at theneedle tip when Doppler interrogation was performed during the processof needle insertion. At pulse repetition frequencies lower than 1000 Hz,an increasing amount of tissue flash was seen with needle movement whichat the lowest settings e.g. 100 Hz was very prominent.

It was found that when a tissue or agar phantom was used, the needleaccumulated material within it and became blocked during insertion. Whenthis occurred, no colour signal was visible at the tip. Blockage wasprevented by using a phantom made of ultrasound coupling jelly.

The 0.406 mm (0.016") internal diameter hollow stylet was connected tothe pressure tubing and inserted into the 20G Chiba needle so that itprotruded just beyond its tip to see if it was possible to conductsignal down a lumen of this diameter. Satisfactory colour signal waseasily visible at the tip of this hollow stylet, although the size ofthe beacon was smaller than when the 20G needle barrel was connecteddirectly to the pressure tubing.

The volume control of both amplifier and signal generator needed to beat maximum in order for good quality signal to be registered.Accordingly the speaker was housed in a cabinet to minimise unwantedsound output. Reducing the volume caused a corresponding reduction incolour signal on the monitor. Of interest is the observation that slightmovement of the transducer off the needle tip resulted in failure todetect any signal. This sensitivity allowed detection of the exactlocation of the tip of the needle in both colour Doppler and spectralmodes. Furthermore the needle tip could be easily found when the probewas displaced far away from the insertion site and aligned randomly withrespect to the needle shaft.

Referring now to FIG. 2, the needle arrangement shown is designed toprevent occlusion of the oscillating fluid column during insertion intothe body tissue and comprises a tubular outer cutting sheath 34 housinga trocar 21. Trocar 21 has a recess 14 at its distal end which exposes aretractable tubular stylet 30 which has a radially directed aperture 32adjacent its forward (distal) tip. The bore of stylet 30 communicateswith the funnel arrangement shown in FIG. 1 via flexible tubing 4 andconsequently the Doppler signal is emitted at aperture 32 throughout theinsertion and enables the precise position of the tip portion of theneedle arrangement to be detected continuously.

In use, first the trocar 21 is advanced together with the stylet 30, thelatter having its aperture 32 located in the recess 14 as shown and theouter cutting sheath being retracted as shown. When the recess 14 hasbeen advanced to the required position, as determined with the aid ofthe Doppler ultrasound image of the stylet tip region, the stylet 30 iswithdrawn from the trocar 21 to allow tissue to fill the recess 14 andouter cutting sheath 34 is advanced (from left to right relative to FIG.2) over the trocar to cut off the tissue lying in recess 14. Theresulting tissue sample can then be extracted. In this manner a tissuesample (e.g. of a liver lesion) can be taken from an accurately knownregion of the tissue.

In all the arrangements illustrated in the drawings, the stylet, cannulaand trocar (if used) as well as the flexible tubing are sterilised andmay be disposable.

The invention also provides a medical apparatus comprising a tubularneedle which is adapted for insertion into body tissue, the needle beingprovided with a transducer which is substantially mechanically isolatedfrom the needle and coupled to a fluid column within the needle, thetransducer being arranged to generate a longitudinal oscillation of saidfluid column at a non-ultrasonic frequency which enhances the visibilityof the needle tip to Doppler ultrasound imaging.

We claim:
 1. A medical needle arrangement for insertion into bodytissue, comprising:a hollow stylet having a bore therein, a distal endsand an exposed aperture positioned about said distal end andcommunicating with said bore, said aperture being located anddimensioned to substantially prevent occlusion of said aperture by bodytissue, said bore and said aperture being configured for emitting asub-ultrasonic longitudinal oscillation therefrom; and a cannula, saidstylet being housed within and slidable relative to said cannula.
 2. Themedical needle arrangement of claim 1 wherein said exposed aperture ofsaid hollow stylet protrudes beyond a distal end of said cannula.
 3. Themedical needle arrangement of claim 1 wherein said distal end of saidhollow stylet includes a closed beveled tip.
 4. The medical needlearrangement of claim 1 wherein said cannula includes a beveled distalend.
 5. The medical needle arrangement of claim 1 wherein said apertureis a radial aperture formed in a wall of said hollow stylet.
 6. Themedical needle arrangement of claim 1 wherein said hollow styletcomprises a tubular stylet.
 7. The medical needle arrangement of claim 1wherein said cannula comprises a trocar having a recess about a distalend thereof and wherein said exposed aperture of said hollow stylet ispositioned in said recess of said trocar for emitting a sub-ultrasoniclongitudinal oscillation therefrom.
 8. The medical needle arrangement ofclaim 7 wherein said exposed aperture comprises a radially directedaperture.
 9. The medical needle arrangement of claim 7 furthercomprising an outer cutting sheath being slidable over said recess ofsaid trocar.
 10. The medical needle arrangement of claim 1 furthercomprising means for applying a sub-ultrasonic longitudinal oscillationto said bore of said hollow stylet.
 11. The medical needle arrangementof claim 1 wherein said cannula includes a bore and wherein saidarrangement further comprises means for applying a sub-ultrasoniclongitudinal oscillation to said bore of said cannula.
 12. The medicalneedle arrangement of claim 1 further comprising means for substantiallymechanically isolating said hollow stylet and said cannula from asub-ultrasonic transducer.
 13. A medical needle arrangement forinsertion into body tissue, comprising:a hollow stylet having a boretherein, a distal end, and an exposed aperture positioned about saiddistal end and communicating with said bore; and a trocar having arecess about a distal end thereof, said stylet being housed within andslidable relative to said trocar, wherein said exposed aperture of saidhollow stylet is positioned in said recess of said trocar for emitting asub-ultrasonic longitudinal oscillation therefrom.
 14. The medicalneedle arrangement of claim 13 wherein said exposed aperture comprises aradially directed aperture.
 15. The medical needle arrangement of claim13 further comprising an outer cutting sheath being slidable over saidrecess of said trocar.
 16. The medical needle arrangement of claim 13further comprising means for applying a sub-ultrasonic longitudinaloscillation to said bore of said hollow stylet.
 17. The medical needlearrangement of claim 13 wherein said distal end of said trocar includesa closed beveled tip.
 18. The medical needle arrangement of claim 13wherein said aperture is a radial aperture formed in a wall of saidhollow stylet.
 19. The medical needle arrangement of claim 13 whereinhollow stylet comprises a tubular stylet.
 20. A medical needlearrangement for insertion into body tissue, comprising:a tubular stylethaving a bore therein, a distal end, and an exposed aperture positionedabout said distal end and communicating with said bore; a trocar havinga recess about a closed, distal end thereof, said tubular stylet beinghoused within and slidable relative to said trocar, wherein said exposedaperture of said tubular stylet is positioned in said recess of saidtrocar for emitting a sub-ultrasonic longitudinal oscillation therefrom;and an outer cutting sheath being slidable over said recess of saidtrocar.